This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-402663, filed Dec. 28, 2000, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an organic electroluminescent device (organic EL device) and a display apparatus, more specifically, to an organic EL device utilizing excited triplet states of a host molecule and a display apparatus using thereof.
2. Description of the Related Art
An organic EL device has features including, self-emission, thin and lightweight form, low electric power consumption, possibility for full color and the like. For these features, the organic EL device is recognized by those skilled in the art as a candidate for coming generation display having a possibility to surpass a liquid crystal display. However, the organic EL device has a drawback of insufficient emission efficiency, and there is a demand for improvement in emission efficiency for, in particular, a red-emitting and blue-emitting organic EL device.
In order to realize an organic EL device having high luminance and long life, an approach utilizing excited triplet states of a host molecule is known. When electrons and holes injected from a pair of electrodes are recombined in a luminescent layer, the host molecules are electronically excited. At that time, a ratio of generation probability of excited singlet states and that of excited triplet states is about 1:3. The excited singlet states contribute to emission by luminescent dye molecules, while the excited triplet states generally do not contribute to emission. However, in the case of using a type of luminescent dye molecule whose energy levels are highly degenerated such as a rare earth metal complex and a linear xcfx80-electron conjugated molecule, the dye molecules can emit light through not only energy transfer from the host molecules in excited singlet states to the dye molecules, but also energy transfer from the host molecules in excited triplet states to the dye molecules. From this viewpoint, an approach is proposed in that rare earth metal complexes are doped into the host molecules, and the energy of the host molecules in the excited triplet states is transferred to the rare earth metal complexes, thereby allowing the rare earth metal ions to emit light (Jpn. Pat. Appln. KOKAI Publication No. 8-319482).
However, conventional host molecules known in the art have significantly lower energy levels in excited triplet states than those in excited singlet states. Therefore, if a luminescent dye molecule is selected so that energy transfer from the host molecules in excited triplet states should be made easily, use efficiency of the energy of the host molecules in excited singlet state will be lowered. As a result, it has been not possible to improve emission efficiency of conventional organic EL devices.
As mentioned above, the conventional organic EL devices cannot utilize both the energy of the host molecules in excited singlet states and the energy of those in excited triplet states in efficient manners, making it impossible to allow the luminescent dye molecules to emit light efficiently.
An object of the present invention is to provide an organic EL device showing high efficiency and long life that can utilize the energies of host molecules both in excited singlet states and in excited triplet states, and a display apparatus employing the organic EL device.
An organic electroluminescent device, comprising: an anode; a cathode; and a polymer luminescent layer disposed between the anode and the cathode, and comprising a host molecule and a luminescent dye molecule, the host molecule being formed of a xcfx80-electron conjugated polymer having carbon-fluorine bond, the luminescent dye molecule being capable of receiving energy from the host molecule both in an excited singlet state and in an excited triplet state.
An organic electroluminescent device, comprising: an anode; a cathode; and a polymer luminescent layer disposed between the anode and the cathode, and comprising a host molecule and a luminescent dye molecule, the host molecule being formed of a xcfx80-electron conjugated polymer having a carbon-fluorine bond, at least one type of luminescent dye molecule being selected from the group consisting of a transition metal complex and a linear xcfx80-electron conjugated molecule.
A display apparatus comprising, pixels arranged in a two-dimensional array, each pixel including multiple types of organic electroluminescent devices different in emission color, each organic electroluminescent device comprising an anode, a cathode, and a polymer luminescent layer disposed between the anode and the cathode; wherein the polymer luminescent layer of at least one type of organic EL device comprises a host molecule and a luminescent dye molecule, the host molecule being formed of a xcfx80-electron conjugated polymer having a carbon-fluorine bond, at least one type of luminescent dye molecule being selected from the group consisting of a transition metal complex and a linear xcfx80-electron conjugated molecule.